GEOLOGY. 331 



matters of observation. A friend who last year visited Iceland, informs me 

 that the last great auks, known with anything like certainty to have been 

 there seen, were two which were taken in 1844, during a visit made to the 

 high rock called " Eldcy," or " Mcelsoekten," lying off Cape Reykianes, the 

 south-west point of Iceland. This is one of three principal rocky islets 

 formerly existing in that direction, of which the one, specially named from 

 this rare bird, " Geirfugla Sker," sank to the level of the surface of the sea 

 during a volcanic disturbance in or about the year 1830. Such disappearance 

 of the fit and favorable breeding-places of the Alca impe.nnis, must form an 

 important element in its decline towards extinction. The numbers of the 

 bones of Alca impennis on the shores of Iceland, Greenland, and Denmark, 

 attest the abundance of the bird in former times. A consideration of such 

 instances of modern partial or total extinctions, may best throw light, and 

 suggest the truest notions, of the causes of ancient extinction. 



As to the successions, or coming in, of new species, one might speculate 

 on the gradual modifiability of the individual ; on the tendency of certain 

 varieties to survive local changes, and thus progressively diverge from an 

 older type; on the production and fertility of monstrous offspring; on the 

 possibility, e. g., of a variety of auk being occasionally hatched with a 

 somewhat longer winglct, and a dwarfed stature; on the probability of such 

 a variety better adapting itself to the changing climate or other conditions 

 than the old type of such an origin of Alca tordo, e. g. ; but to what 

 purpose? Past experience of the chance aims of human fancy, unchecked 

 and unguided by observed facts, shows how widely they have ever glanced 

 away from the gold centre of truth. 



As the result of the evidence accumulated by geologists, I have affirmed 

 that the successive extinction of Amphitheria, Spalacotheria, Triconodons, 

 and other mesozoic forms of mammals, has been followed by the introduc- 

 tions of much more numerous, varied, and higher organized forms of the 

 class, during the tertiary periods. There are, however, geologists who main- 

 tain that this is an assumption, based upon a partial knowledge of the facts. 

 Mere negative evidence, they allege, can never satisfactorily establish the 

 proposition that the mammalian class is of late introduction, nor prevent 

 the conjecture that it may have been as richly represented in secondary, as 

 in tertiary times, could we but get evidence of the terrestrial Fauna of the 

 oolitic continent. To this objection I have to reply: in the palaeozoic strata, 

 which, from their extent and depth, indicate, in the earth's existence as a 

 seat of organic life, a period as prolonged as that which has followed their 

 deposition, no trace of mammals has been observed. It may be conceded 

 that, were mammals peculiar to dry land, such negative evidence would 

 weigh little in producing conviction of their non-existence during the Silurian 

 and Devonian reons, because the explored parts of such strata have been 

 deposited from an ocean, and the chance of finding a terrestrial and air- 

 breathing creature's remains in oceanic deposits is very remote. But, in the 

 present state of the warm-blooded, air-breathing, viviparous class, no genera 

 and species arc represented by such numerous and widely dispersed individ- 

 uals, as those of the order Cetacea, which, under the guise of fishes, dwell, 

 and can only live, in the ocean. In all Cetacea the skeleton is well ossified, 

 and the vertebrae are very numerous: the smallest Cetaceans would be 

 deemed large amongst land mammals, the largest surpass in bulk any 

 creatures of which we have yet gained cognizance; the hugest ichthyosaur, 

 iguanodon, megalosaur, mammoth, or megathere, is a dwarf in comparison 



